Buggy code:
final class CommandSets { private static final Map < String , CommandSet > commandSetMap = CommandSets . initializeCommandSetMap ( ) ; private CommandSets ( ) { } @ NotNull private static Map < String , CommandSet > initializeCommandSetMap ( ) { } private static CommandSet initializeDefaultCommandSet ( ) { CommandSet commandSet = CommandSet . emptyCommandSet ( ) ; commandSet . addCommand ( new Command ( "achievements" , "Displays<seq2seq4repair_space>the<seq2seq4repair_space>already<seq2seq4repair_space>unlocked<seq2seq4repair_space>achievements." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { AchievementTrackerWriter . parseCommand ( arguments ) ; } } ) ; commandSet . addCommand ( new Command ( "age" , "Displays<seq2seq4repair_space>the<seq2seq4repair_space>character's<seq2seq4repair_space>age." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { Game . getGameState ( ) . getHero ( ) . printAge ( ) ; } } ) ; commandSet . addCommand ( new Command ( "cast" , "Casts<seq2seq4repair_space>a<seq2seq4repair_space>spell." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { Game . getGameState ( ) . getHero ( ) . getSpellcaster ( ) . parseCast ( arguments ) ; } } ) ; commandSet . addCommand ( new Command ( "destroy" , "Destroys<seq2seq4repair_space>an<seq2seq4repair_space>item<seq2seq4repair_space>on<seq2seq4repair_space>the<seq2seq4repair_space>ground." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { Game . getGameState ( ) . getHero ( ) . destroyItem ( arguments ) ; } } ) ; commandSet . addCommand ( new Command ( "drop" , "Drops<seq2seq4repair_space>the<seq2seq4repair_space>specified<seq2seq4repair_space>item." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { Game . getGameState ( ) . getHero ( ) . dropItem ( arguments ) ; } } ) ; commandSet . addCommand ( new Command ( "eat" , "Eats<seq2seq4repair_space>an<seq2seq4repair_space>item." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { Game . getGameState ( ) . getHero ( ) . eatItem ( arguments ) ; } } ) ; commandSet . addCommand ( new Command ( "equip" , "Equips<seq2seq4repair_space>the<seq2seq4repair_space>specified<seq2seq4repair_space>item." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { Game . getGameState ( ) . getHero ( ) . parseEquip ( arguments ) ; } } ) ; commandSet . addCommand ( new Command ( "exit" , "Exits<seq2seq4repair_space>the<seq2seq4repair_space>game." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { Game . exit ( ) ; } } ) ; commandSet . addCommand ( new Command ( "go" , "Makes<seq2seq4repair_space>the<seq2seq4repair_space>character<seq2seq4repair_space>move<seq2seq4repair_space>in<seq2seq4repair_space>the<seq2seq4repair_space>specified<seq2seq4repair_space>direction." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { <START_BUG> Engine . parseHeroWalk ( arguments ) ; <END_BUG> } } ) ; commandSet . addCommand ( new Command ( "items" , "Lists<seq2seq4repair_space>the<seq2seq4repair_space>items<seq2seq4repair_space>in<seq2seq4repair_space>the<seq2seq4repair_space>character's<seq2seq4repair_space>inventory." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { Game . getGameState ( ) . getHero ( ) . printInventory ( ) ; } } ) ; commandSet . addCommand ( new Command ( "kill" , "Attacks<seq2seq4repair_space>the<seq2seq4repair_space>target<seq2seq4repair_space>chosen<seq2seq4repair_space>by<seq2seq4repair_space>the<seq2seq4repair_space>player." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { Game . getGameState ( ) . getHero ( ) . attackTarget ( arguments ) ; } } ) ; commandSet . addCommand ( new Command ( "load" , "Loads<seq2seq4repair_space>a<seq2seq4repair_space>saved<seq2seq4repair_space>game." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { GameState loadedGameState = Loader . parseLoadCommand ( arguments ) ; if ( loadedGameState != null ) { Game . unsetGameState ( ) ; Game . setGameState ( loadedGameState ) ; } } } ) ; commandSet . addCommand ( new Command ( "look" , "Describes<seq2seq4repair_space>what<seq2seq4repair_space>the<seq2seq4repair_space>character<seq2seq4repair_space>can<seq2seq4repair_space>see." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { Game . getGameState ( ) . getHero ( ) . look ( null ) ; } } ) ; commandSet . addCommand ( new Command ( "map" , "Shows<seq2seq4repair_space>a<seq2seq4repair_space>map<seq2seq4repair_space>of<seq2seq4repair_space>your<seq2seq4repair_space>surroundings." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { WorldMapWriter . writeMap ( WorldMap . makeWorldMap ( ) ) ; } } ) ; commandSet . addCommand ( new Command ( "milk" , "Attempts<seq2seq4repair_space>to<seq2seq4repair_space>milk<seq2seq4repair_space>a<seq2seq4repair_space>creature." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { Game . getGameState ( ) . getHero ( ) . parseMilk ( arguments ) ; } } ) ; commandSet . addCommand ( new Command ( "new" , "Starts<seq2seq4repair_space>a<seq2seq4repair_space>new<seq2seq4repair_space>game." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { Game . unsetGameState ( ) ; Game . setGameState ( Loader . newGame ( ) ) ; } } ) ; commandSet . addCommand ( new Command ( "pick" , "Attempts<seq2seq4repair_space>to<seq2seq4repair_space>pick<seq2seq4repair_space>up<seq2seq4repair_space>an<seq2seq4repair_space>item<seq2seq4repair_space>from<seq2seq4repair_space>the<seq2seq4repair_space>current<seq2seq4repair_space>location." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { Game . getGameState ( ) . getHero ( ) . pickItem ( arguments ) ; } } ) ; commandSet . addCommand ( new Command ( "read" , "Reads<seq2seq4repair_space>the<seq2seq4repair_space>specified<seq2seq4repair_space>item." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { Game . getGameState ( ) . getHero ( ) . readItem ( arguments ) ; } } ) ; commandSet . addCommand ( new Command ( "rest" , "Rests<seq2seq4repair_space>until<seq2seq4repair_space>healing<seq2seq4repair_space>about<seq2seq4repair_space>three<seq2seq4repair_space>fifths<seq2seq4repair_space>of<seq2seq4repair_space>the<seq2seq4repair_space>character's<seq2seq4repair_space>health." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { Game . getGameState ( ) . getHero ( ) . rest ( ) ; } } ) ; commandSet . addCommand ( new Command ( "save" , "Saves<seq2seq4repair_space>the<seq2seq4repair_space>game." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { Loader . saveGame ( Game . getGameState ( ) , arguments ) ; } } ) ; commandSet . addCommand ( new Command ( "saves" , "Displays<seq2seq4repair_space>a<seq2seq4repair_space>table<seq2seq4repair_space>with<seq2seq4repair_space>all<seq2seq4repair_space>the<seq2seq4repair_space>save<seq2seq4repair_space>files." ) { @ Override public void execute ( @ NotNull String [ ] arguments ) { SavesTableWriter . writeSavesFolderTable ( ) ; } } ) ;

Fix:
Game . getGameState ( ) . getHero ( ) . walk ( arguments ) ;